- Cosmic Mystery Solved?

SCIENCE AND MEDICINE - SCOPE

October 27, 1991

A cosmic mystery got a little more down-to-Earth recently. In the 20 years since scientists discovered that the heavens are pervaded by a background crackle of X-rays that originate somewhere outside our galaxy, astronomers have puzzled over possible sources. Now a team of British and U.S. researchers, using data from the Rosat X-ray satellite, reports in the journal Nature that much - and maybe all - of the cosmic background radiation comes from quasars, which are enormously distant starlike objects. When dust and gas spiral into the quasar's gravitational maw, they experience such frictional heating that they emit X-rays. The Rosat studies found 39 X-ray-emitting quasars in only one-third of one square degree of the sky. If that distribution is typical, the authors conclude, it would be enough to ''account for almost all of the X-ray background'' at key frequencies.